In recent years there has been much progress in the area of cohort sampling which has led to new types of case-control type study designs. The theory underlying nested case-control sampling and population based case-control studies is now well understood and useful new designs have been developed. Among these are variants of nested case-control sampling which allow for restricted control selection, stratified sampling, a variable number of controls per case, simple and stratified versions of case-cohort sampling, two-stage designs and randomized recruitment. These new designs have great potential application in special situations. Yet there seems to be little awareness of the new methods themselves, little understanding of when these methods are potentially useful, this new technology has not been implemented into computer software to facilitate the design, conduct, or analysis of a sampled-cohort substudy. We are proposing to develop two products under this grant, the first is computer software and the second is a textbook-teaching software. Thus, the specific aims for the entire project (Phases I and II are: 1. To develop software to facilitate the design, conduct, and analysis of studies using the new designs. These will be included as modules into the Epicenter Software products Epilog Plus and Power. 2a. To write a textbook on cohort sampling methods for a graduate level course or self instruction. 2b. To develop software examples and exercises (SEEs) to illustrate the methods presented in the book. Data sets (mostly derived from NIH-funded studies) will be used to illustrate the techniques described in the book.